Some types of rotary machine tools such as twist drills and reaming tools are configured to advance into a workpiece in a direction generally aligned with the axis of rotation of the rotary machine tool. In other words, such tools are designed to drill or bore into a body, the primary feed direction being substantially aligned with the axis of rotation. Other types of machine tools such as end mill tools and router tools are configured to advance side-on into a workpiece, the primary feed direction being substantially non-aligned with the axis of rotation (or even substantially laterally with respect to the axis of rotation). Rotary tools having a relatively small diameter may be too small to be made by clamping or brazing a sufficient number of inserts onto a tool body sufficiently precisely or robustly. A further disadvantage of brazing segments onto tools is that there may be a practical limitation on the closeness of the spacing between cutting edges on a side cutting surface. For example, it may be difficult for all but experimental tools to have superhard cutting edges spaced apart on a side cutting surface closer than about 10 mm. Consequently, there may be a practical limitation on the number of cutting edges which can be achieved on a tool, particularly a rotary tool, which may limit the productivity that may be achieved using the tool. In the case of metal cutting, tool productivity may be primarily determined by the product of the chip load per cutting edge and the number of cutting edges.
European patent number 1 351 798 discloses a method of producing a cutting tool, the method including providing an unbonded assembly comprising a cylindrical core having ends and an elongate side surface covered partially or completely by an unsintered layer of ultra-hard abrasive particles, and sintering the unbonded assembly to provide a product comprising a cylindrical core and an ultra-hard abrasive material bonded to the core. The sintered product is then worked to produce one or more cutting edges in the ultra-hard abrasive material.
While a greater number of cutting edges may improve the efficiency of a machine tool in use, the cost and complexity of providing a greater number of cutting edges is likely to be relatively high, especially in the case of relatively small rotary cutter elements.